1. Field of the Invention
The present disclosure relates to header sub-assemblies, and more particularly to header sub-assemblies suitable for high-temperature applications.
2. Description of Related Art
There are a variety of dielectric header sub-assemblies for mounting a semiconductor die, e.g. a sensor. Traditionally, the header sub-assemblies include a ceramic insulating header body containing electrical connectors and a metal ring surrounding the outer diameter of the header body for support and for hermetic isolation of the sensor environment from the completed package. For high temperature applications, the header body is brazed to the metal ring and to the electrical connectors at a high temperature. Compressive stresses imposed on the header body by the metal ring upon cooling from the braze temperature can cause the surface of the header where the die is mounted to distort, e.g. in the concave and/or convex direction.
One solution for the surface deformation is to grind the concave and/or convex surface flat at room temperature after brazing. While this solution alleviates the curvature at room temperature, deformities can still occur during in-service temperature cycling, thereby exerting stresses on the sensor attachment to the header surface and causing issues with die performance. For example, micro-cracks can occur in the attachment between the die and the ceramic header body.
In addition, cracking can occur between the electrical connector and the header body along the braze joint due to differences in thermal expansion. Further, in order to braze a metallic part to a ceramic part, the ceramic part is typically coated with a thick film ink, e.g. molybdenum and/or tungsten. These metals oxidize at 400° C. and are not always suitable for certain applications. Sputtered metallic films are also an option for brazing a metallic part to a ceramic part. Sputtered metallic films can be used so that the braze filler can wet the surface of the ceramic by wicking along the joint via capillary action. This can be difficult and time consuming when brazing, for example, small pin holes, such as those used for the electrical connectors.
Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for header sub-assemblies that mitigate deformities and cracking due to thermal stresses and increase ease of manufacturing. The present invention provides a solution for these problems.